The optical amplifier is an essential device for the optical fiber communication system, which amplifies the intensity of the signal light transmitted within the optical fiber after it is naturally declined to keep it on a certain standard.
In consideration of the cost, the erbium-doped optical fiber amplifier is the worthiest in the market. The operation of the erbium-doped optical fiber amplifier is to firstly excite the electron in the 4f shell of the erbium ion doped in the optical fiber to an excitation state by a pump laser light. When the signal light passes through the erbium-doped optical fiber, the electron in the excitation state is stimulated by an incident photon to give laser emission having the same wavelength, polarization, as well as phase with that of the incident photon. This results in the optical gain or the amplifying effect.
However, the conventional erbium-doped optical fiber amplifier based on evanescent excitation method has a limited optical gain or amplifying effect due to the limited effective operation length. Please refer to FIG. 1, which shows the conventional method where the slant grating is used to reflect the pumping light in the optical fiber to the side having the optical-gain medium so as to generate the optical gain. Besides, the side-polishing can also be used to expose signal light and pumping light in the optical fiber to the side having the optical-gain medium. No matter which method is used, the effective interaction length between the gain medium and signal/pump lights is limited. This relatively limits the optical gain or the amplifying effect.
In order to overcome the drawbacks in the prior art, a cladding-pumped evanescent gain optical fiber is provided. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the present invention has the utility for the industry.